Sources told CBS News' Senior Investigative Producer Pat Milton the multi-page typed note was a philosophical rant of someone who was mad at the world. The source said the note was focused a great deal on the suspect's low opinion of himself.

Oregon college shooter appeared ready for gun battle to the end

Milton reports that throughout the writings, the suspect obsesses about himself and his place in the world, which he apparently did not think was very good. Mercer had also apparently taken a creativity or writing course at Umpqua Community College. There is no indication that the suspect was affiliated with any group. And his motive is still unclear.

Authorities investigating the shooting say they have found a number of firearms at the gunman's apartment and CBS News correspondent Jeff Peques reports that one of the guns recovered at the scene of the shooting is not registered to the gunman.

Officials say Harper opened fire at Umpqua Community College Thursday, killing nine people and wounding nine others others before dying during an exchange of gunfire with officers. Authorities said Friday that 13 weapons had been recovered - six at the scene of the shooting and seven at the gunman's residence.

A statement from Eibel's family says he volunteered at a wildlife center and animal shelter. He was studying chemistry and loved to play soccer. Cooper's family says he was funny and compassionate and loved dancing and voice acting. A statement from Johnson's family says he was a Christian and recently enrolled in school.

ATF Assistant Special Agent in Charge Celinez Nunez said at a news conference Friday that all of the weapons were purchased legally, seven of them by the shooter or his family members in the last three years. She says investigators also found a flak jacket next to a rifle at the school, which contained steel plates.

Douglas County Sheriff John Hanlin said early Friday that investigators were at the college and Mercer's nearby apartment throughout the night.

Pegues reports that the guns included a 9mm Glock pistol and .40-caliber Smith & Wesson, both traced to the suspect. He also had a .40-caliber Taurus pistol traced to someone in Portland, as well as body armor.

Investigators are still trying to determine how the gunman obtained a .556 caliber rifle, which is similar to an AR-15, Pegues reports.

A law enforcement source told CBS News senior investigative producer Pat Milton that it is unclear if the gunman was actually wearing the bullet-proof vest when he was fatally shot or had it with him.

Hanlin also says investigators went door to door in the neighborhoods near the college and the shooter's apartment to try to learn more details.

Army veteran hailed as hero in Oregon shooting

Peques reports that a receipt from the campus store was also found at the shooting scene and investigators believe it belonged to Mercer.

The U.S. Army said Mercer flunked out of basic training in 2008. Lt. Col. Ben Garrett, an Army spokesman, said Mercer was in service at Ft. Jackson, South Carolina, starting on Nov. 5, 2008. But by Dec. 11, 2008, he was discharged for failing to meet the minimum administrative standards.

Social media profiles linked to Mercer suggested he was fascinated by the IRA, frustrated by traditional organized religion and tracked other mass shootings.

Carmen Nesnick, the stepsister of Mercer, said her stepbrother was not a religious nor anti-religious person and that her family is Christian.

"All he ever did was put everybody before himself. He wanted everyone to be happy. No matter if he was sad or mad, he would always try to cheer up everybody," she said.

There didn't seem to be many recent connections on the social media sites linked to Mercer, with his MySpace page just showing two friends. He appeared to have at least one online dating profile.

On a torrents streaming site and blog that appeared to belong to Mercer, posts referenced multiple shootings and downloads included several horror films and a documentary on a mass shooting at Sandy Hook Elementary School in Newtown, Connecticut.

In one post on the blog about Flanagan, Mercer apparently wrote, "I have noticed that so many people like [Flanagan] are alone and unknown, yet when they spill a little blood, the whole world knows who they are. A man who was known by no one, is now known by everyone. His face splashed across every screen, his name across the lips of every person on the planet, all in the course of one day. Seems like the more people you kill, the more you're in the limelight."

Stories of heroism emerge amidst Oregon college shooting tragedy

A MySpace page that appeared to belong to Mercer included several photos and graphics of the Irish Republican Army as well as a picture of Mercer holding a rifle.

Meanwhile, a doctor said one victim of the deadly mass shooting will likely be released from a hospital Friday.

Dr. Jason Gray of Mercy Medical Center says the hospital in Roseburg, which is 180 miles south of Portland, received 10 patients Thursday - one died, two were quickly treated and released and three were transferred to a hospital near Eugene for a higher level of care.

Of the four remaining patients, one was discharged late Thursday, and one was expected to leave Friday. Gray says the other two are expected to survive, but one remains in critical condition.

The three patients who needed additional care were transferred to PeaceHealth Sacred Heart Medical Center at RiverBend. The Eugene-area hospital said Friday that two patients were stable, one was moving out of the ICU and all three were expected to survive.